It is often necessary or desirable to measure various parameters of blood, such as temperature and blood constituents, such as blood gases, pH, other electrolytes and glucose. This can be accomplished in real time using fluorescent sensors. For example, this can be accomplished in an extracorporeal blood loop as shown in Cooper Application Ser. No. 546,493 filed on Oct. 28, 1983, and in vivo as disclosed in Lubbers et al Reissue Pat. No. 31,879. For in vivo sensing, a probe or catheter carrying an appropriate sensor is inserted into a blood vessel of the patient.
One of the most important gases that needs to be sensed is oxygen. One problem with in vivo oxygen sensing is that the readings obtained for the concentrations of oxygen tend to vary over an unacceptably wide range when compared with the results obtained using conventional laboratory techniques for measuring the concentration of oxygen. It has been found that this deviation is in many cases unacceptably large so that the reliability of the in vivo measuring system is called into question.